1. Field of the Invention
This invention relates to a method for producing a heavy crude oil from a subterranean formation via a wellbore, mixing the heavy crude oil with a diluent, transporting the heavy crude oil/diluent mixture to a market location and distilling the mixture to produce a product distillate hydrocarbon stream suitable for pipelining or refining and recovering added values from the residual portions of the heavy crude oil as heat, electricity, steam or synthetic liquid hydrocarbons. The diluent may be recovered as a product stream from the distillation.
2. Description of Related Art
In many parts of the world heavy crude oils are available for production in remote locations. In such instances, the only option may be to transport the heavy crude in a pipeline, by truck, ship or the like to a market location where a market exists for a distillate hydrocarbon stream. Many of the heavier components contained in the heavy crude oil may not be suitable for distillation into distillate hydrocarbon products and may eventually be converted into asphalt, petroleum coke or the like.
In less industrialized parts of the world there may be little market for such products. As a result the products may be of low value in the accessible marketplace. Alternatively, the heavier components may be blended with lighter oils to produce a heavy fuel oil product. Typically, the market value of such heavy fuel oils is relatively low, especially, when the value of the diluent oil as a distillate product is considered.
Many such heavy crude oils are so viscous that it may be difficult to recover such heavy crude oils from a subterranean formation initially without admixture of a diluent with the heavy crude oil in the wellbore to reduce the viscosity of the heavy crude oil. Even if the heavy crude oil is at an elevated temperature in the subterranean formation which is high enough to result in a flowable heavy crude oil at the elevated temperature the heavy crude oil remains likely to cool and solidify in upper portions of the producing well, especially during any periods where production is stopped for an interval. Similarly the heavy crude oil is likely to cool and solidify in surface pipelines unless required temperatures and flowrates in the surface pipelines can be maintained. As a result distillate hydrocarbon diluents or other suitable diluents may be mixed with such heavy crude oils either during or after production and before pipelining over long distances to prevent solidification of the heavy crude oil in the pipeline. The cost of the diluent is a significant part of the total cost of producing and transporting the heavy crude oil.
Such heavy crude oils contain a much higher percentage of non-distillable components than lighter crude oils. Some such heavy crude oils may contain less than 50 weight percent distillable hydrocarbons.
The production and transportation of such heavy crude oils, especially in remote locations, requires that large quantities of diluent be transported to the remote location via pipeline, truck or the like. This diluent is expensive relative to the heavy crude oil even without considering the added transportation cost. The diluent when mixed with the heavy crude oil may result in a mixture which still contains as much as 45 weight percent residual (non-distillable) materials. Even if transported to a refinery the residual materials are of little value and are typically charged to a petroleum coker or used as asphalt and the like. Typically such heavy crude oils also have a high metals content in the residual materials which reduces the value of any petroleum coke produced from such residual materials.
These considerations may result in many heavy crude oils at remote locations being uneconomical to produce and market. Accordingly, a continuing search has been directed to methods for producing such heavy crude oils at remote sites and marketing valuable distillable hydrocarbons and the like economically.